This invention relates to a process for the production of benzothiazolyl-2-sulphenamides from 2-mercaptobenzothiazoles or dibenzothiazolyl-2,2'-disulphides and primary or secondary amines in the presence of oxygen and a copper-containing catalyst in a solvent.
Sulphenamides are used in large quantities as vulcanization accelerators.
There are several known processes for the production of sulphenamides. On an industrial scale, they are produced by the oxidative condensation of 2-mercaptothiazoles with an amine using such oxdizing agents as, for example, chlorine, iodine or hypochlorite, hydrogen peroxides or other peroxides (E. L. Carr, J. Org. Chem. 14 921 (1948), U.S. Pat. Nos. 2,191,657, 2,417,989, 2,419,283, 3,144,652, French Pat. No. 841,753, British Pat. No 655,668 and German Offenlegungsschrift No. 31 27 193). In addition, it is known that sulphenamides may be obtained by replacing the amide in an N-substituted thiazolyl-2-sulphenamide by another amide (Offenlegungsschrift No. 19 41 884), by the ammonolysis of dithiazolyl disulphide (British Pat. No. 377,370, U.S. Pat. Nos. 2,100,692, 2,214,460 and 2,226,767) and also by electrochemical oxidation (Offenlegungsschrift No. 27 44 423; and J. Org. Chem. 43 (16) 3223 (1978)).
It is also known that oxygen may be used as an oxidizing agent in the oxidative reaction of 2-mercaptothiazoles or dithiazolyl-2,2'-disulphides with an amine. In the processes according to Canadian Pat. No. 863,531, U.S. Pat. No. 3,737,431 and European Patent Application No. 29 718, metal phthalocyanines are used as the catalyst. However, problems are involved in the industrial production and handling of such catalysts as these which are both sensitive and expensive. In addition, the processes according to these three publications only give moderate to poor yields or involve elaborate process steps for isolating the end product.
In addition, it is known from German Offenlegungsschrifts Nos. 23 49 934 and 23 56 686 (to which U.S. Pat. No. 4,182,873 substantially corresponds), that the reaction of 2-mercaptothiazoles or dithiazolyl-2,2'-disulphides with amines may be carried out in the presence of oxygen and copper or another of its derivatives such as the copper phthalocyanine complexes. Temperatures of from 0.degree. to 200.degree. C. and oxygen partial pressures of from 0.1 to 30 bars are preferably applied in that process. In addition, the reaction is said to be preferably carried out in water or an organic solvent, the solvent used being said to be in particular the excess of the amine used for the reaction with the 2-mercaptobenzothiazole. As the Comparison Examples of these two German Offenlegungsschrifts show, however, these known processes only give relatively low yields of sulphenamide. As further studies have shown, this is quite clearly attributable to the fact that, under the conditions applied, the sulphenamide formed is further oxidized to a considerable extent to secondary products (for example benzothiazolyl sulphonic acids, benzothiazole, sulphates, etc.). In this process, therefore, part of the valuable end product is lost. Accordingly, the selectivities obtainable in this process are totally inadequate for economic application.